Architectural aluminum alloy material and process for manufacturing the same

ABSTRACT

There is provided an architectural Al alloy material which undergoes minor loss of proof stress even after a baking finish treatment at a high temperature of 260 to 280° C. and which can be subjected to acute-angle bending, as well as, a process for manufacturing the same. This architectural Al alloy material, which is a hot rolled JIS A3003 material, contains a fiber structure and a recrystallized grain structure having an area ratio of 20 % or less after a baking finish treatment at 300° C. or lower, and undergoes a proof stress loss of 10% or less after the baking finish treatment. The Al alloy material is manufactured only by hot rolling which is carried out under control such that the temperature at the end of rolling be in the range of 290 to 340° C.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an architectural aluminum (Al)alloy material and a process for manufacturing the same. Morespecifically, the present invention relates to an architectural Al alloymaterial, which is to be put into practical uses as a building materialwith the premise that it is subjected to a baking finish treatment in ahigh temperature region of 260 to 280° C. and which undergoes minor lossof proof stress and retains sufficient elongation even after the bakingfinish treatment to show excellent bendability, as well as, to a processfor manufacturing the same.

[0003] 2. Prior Art

[0004] Since Al alloy materials are light, they are used as exteriorwall materials and interior finishing materials for high-rise buildingsor as curtain wall materials.

[0005] In such cases, an Al alloy plate 1 is subjected to 90-degreebending, for example, as shown in FIG. 1. These days, acute-anglebending is on the increase to bend Al alloy plates by beyond 90°(θ>90°), as shown in FIG. 2. In such acute-angle bending treatments, itis pursued to enhance ornamental design by forming a sharp bend 2. Anexample of bending treatment is shown in FIG. 3, in which a notch 3 isformed on an Al alloy material 1, and the alloy material 1 is bent alongthis notch 3.

[0006] Before the Al alloy material 1 is bent as described above, it issubjected to a baking finish treatment using a coating material such asa fluorine coat, an acrylic resin coating and a urethane resin coatingat a predetermined temperature so as to enhance decorative design andcorrosion resistance of the material 1.

[0007] Those architectural Al alloy materials practically used accordingto such a mode are required to show the following performances:

[0008] First, since they are building materials, they should showappropriate strength properties even after application. Morespecifically, in the case where an Al alloy material is used as anexterior wall material for buildings, it is required to have a proofstress of 95 N/mm² or more even after application.

[0009] Further, they are required to have appropriate elongationproperties to enhance smooth bending treatment and form sharp angles atbends.

[0010] As architectural Al alloy materials, for example, A3004-H24 (3004defined by B209 of ASTM) and A3004-H32 (3004 defined by B209 of ASTM)materials have conventionally been used, primarily in view of theirstrength properties.

[0011] In manufacturing such materials, an Al alloy material ofpredetermined specifications is melted first to form an ingot thereof.The ingot is then subjected to a soaking treatment at a predeterminedtemperature for a predetermined time, followed by a hot rollingtreatment at a predetermined processing rate.

[0012] In this hot rolling process, the solidification structure of theingot is converted into a fiber structure as it is rolled out in therolling direction.

[0013] Subsequently, the resulting rolled alloy material is subjected tocold rolling to effect finely dividing of the crystal grains andthickness adjustment, and after the alloy material is annealed to removeprocessing strain, it is subjected again to cold rolling and heattreatment for removing the strain occurred in the cold rolling. The thustreated Al alloy material is used in practical applications.

[0014] Here, in the series of steps in the manufacturing processdescribed above, rolling strains accumulate in the workpiece at the endof the hot rolling treatment and cold rolling treatment. When theresulting workpiece is then heated to a temperature not lower than therecrystallization temperature thereof, the energy of processing straintriggers growth of grains of recrystallization in the structure. Eachgrain of the recrystallized structure usually does not assume the formof fiber but of a grain of a certain size.

[0015] The A3004-H24 material and the like described above are thosewhich are all subjected finally to the cold rolling treatment, so thatthey have finely divided grains of recrystallized structure. Inaddition, fiber structures remain in these materials, so that they canbe subjected to sharp 90-degree bending.

[0016] When they are subjected to more than 90-degree acute-anglebending and cracking occurs at the bends of the alloy materials, thecracked portions are mended by welding.

OBJECT AND SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to provide anarchitectural Al alloy material used as a building material on thepremise that it is subjected to baking finish treatment, whereincracking does not occur even when it is subjected to sharp bending oracute-angle bending, since it undergoes minor loss of the proof stressand also has appropriate elongation properties even after the bakingfinish treatment, and to provide a process for manufacturing it.

[0018] In order to attain the above object, the present inventionprovides an architectural Al alloy material, which is a hot rolledmaterial defined by JIS A3003 (3003 defined by B209 of ASTM); thematerial containing, in terms of a structure after a baking finishtreatment at a temperature of not higher than 300° C., a fiber structureand a recrystallized grain structure having an area ratio of 20% orless; wherein the material undergoes a proof stress loss of 10% or lessafter the baking finish treatment.

[0019] The present invention also provides a process for manufacturingan architectural Al alloy material including the steps of subjecting aningot of JIS A3003 (3003 defined by B209 of ASTM) to a soakingtreatment; and subjecting the resulting ingot to hot rolling to becarried out in such a way that it has a temperature of 290 to 340° C. atthe end of rolling; wherein the thus treated ingot is as such applied toa practical use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic drawing showing 90-degree bending of a platematerial;

[0021]FIG. 2 is a schematic drawing showing acute-angle bending of aplate material;

[0022]FIG. 3 is a schematic drawing showing 90-degree bending of anotched plate material;

[0023]FIG. 4 shows a photomicrographic structure of a plate material inExample 9;

[0024]FIG. 5 shows a photomicrographic structure of a plate material inComparative Example 8;

[0025]FIG. 6 is a schematic view of a plate material bent at rightangles to the rolling direction; and

[0026]FIG. 7 is a schematic view of a plate material bent parallel tothe rolling direction.

DETAILED DESCRIPTION

[0027] The Al alloy material according to the present invention isprepared merely by subjecting an A3003 material having excellentstrength properties to a hot rolling treatment under the conditions tobe described later and is put into practical uses directly after thetreatment. In other words, unlike the conventional Al alloy materials,the alloy material of the present invention is not manufactured by goingthrough the hot rolling, followed by cold rolling, process annealing,cold rolling and heat treatment.

[0028] The Al alloy material of the present invention is manufacturedtypically as follows:

[0029] First, an A3003 material having a predetermined composition ismelted to form an ingot thereof. The ingot is then subjected to soakingand then to hot rolling.

[0030] The soaking treatment is preferably carried out in a temperaturerange of 500 to 630° C. for about 1 to 15 hours. If the soakingtreatment is carried out at a temperature of lower than 500° C.,intermetallic compounds containing substantially, for example, AlMndecreases in quantity, and grains of recrystallized structure growingfrom the solidification structure are coarsened, to be likely to causedrop in bendability of the material and to mar appearance thereof.Further, if the soaking treatment is carried out at a temperature ofhigher than 630° C., deformation, blisters and the like occur in theingot, which are causative of structural defects in the subsequent step(hot rolling). Therefore, the soaking treatment is carried outpreferably at a temperature of 600 to 630° C.

[0031] Meanwhile, if the soaking treatment is carried out for less thanone hour, the ingot cannot be soaked entirely, making it difficult tocarry out homogeneous hot rolling. On the other hand, even if thesoaking treatment is carried out for more than 15 hours, the soakingeffect is saturated, and it is nothing but waste of thermal energy,uneconomically. The soaking treatment is desirably carried out for 2 to6 hours.

[0032] The ingot having undergone the soaking treatment as describedabove is then subjected immediately to hot rolling, where thesolidification structure of the ingot is converted to a fiber structureand also finely divided secondary structure (subgrains) is caused togrow.

[0033] The A3003 material according to the present invention can be putinto practical uses as a building material directly after completion ofthe hot rolling treatment. Therefore, at the point when the material isput into a practical use, the thus hot-rolled A3003 material assumessubstantially the fiber structure formed by the rolling treatment andhas a predetermined amount of finely divided secondary structuredispersed therein.

[0034] This A3003 material having the structure as described aboveexhibits the following effects:

[0035] For example, in carrying out acute-angle bending, if the materialhas the fiber structure only, cracking or the like can occur at the bendalong the grain boundary of the fiber structure. However, the A3003material of the present invention contains the finely divided secondarystructure, so that such cracking can be prevented from occurring. Inother words, the material ensures acute-angle bending.

[0036] In addition, in the case of the A3003 material, even if it issubjected to a baking finish treatment at a high temperature of 300° C.or lower, more typically at 260 to 280° C., % loss of proof stress afterthe baking finish treatment is controlled to 10% or less. Even after thebaking finish treatment of the material, it secures an absolute proofstress value of 95 N/mm² or more, satisfying requirements for theexterior wall material for buildings. Besides, elongation of thematerial is increased to 27% or more, enabling excellent bendingtreatment.

[0037] The properties described above, particularly that % loss of proofstress after the baking finish treatment is controlled to 10% or lessare the effects to be brought about by the finely divided structure andthe fiber structure coexisting in the material. This secondary structurenaturally grows into recrystallized grain structure during the bakingfinish treatment at a high temperature to have increased diametersrespectively, and also the quantity of precipitated crystal grainsthereof increases.

[0038] However, in the case of the A3003 material according to thepresent invention, it is controlled so that it contains therecrystallized grain structure in an amount of not more than 20% of theentire structure in terms of area ratio even after the baking finishtreatment, and that the rest remains as the fiber structure. Thus, lossof proof stress to be caused by the baking finish treatment can be heldwithin 10%.

[0039] Such attribute can be realized by controlling the hot rollingtreatment such that the temperature of the workpiece be in the range of290 to 340° C. at the end of the treatment.

[0040] If the temperature at the end of rolling is higher than 340° C.,the workpiece comes to have an elongation of about 35%. However, it issubstantially of the recrystallized grain structure, which causes roughsurface at the bend.

[0041] Meanwhile, if the temperature at the end of rolling is lower than290° C., the finely divided secondary structure to be formed decreasesin quantity, and the elongation becomes smaller than 27%, inducingcracking in acute-angle bending.

[0042] In order to control the temperature at the end of rolling to bein the range of 290 to 340° C., the temperature at the beginning ofrolling is set to be in the range of 350 to 450° C.

[0043] A temperature at the beginning of rolling of lower than 350° C.cannot secure a temperature of 290° C. or higher at the end of rolling.This can increase the strength but reduces elongation, causing crackingand the like in bending.

[0044] Meanwhile, if the temperature at the beginning of rolling ishigher than 450° C., it is difficult to attain a temperature of 340° C.or lower at the end of rolling. At the end of rolling, coarse grains ofrecrystallized structure predominate the material to cause rough surfaceat a bend in a bending treatment. In addition, the resulting workpiececomes to have a proof stress of smaller than 95 N/mm².

EXAMPLE Examples 1 to 16, Comparative Examples 1 to 9

[0045] (1) Al Alloy Material

[0046] Al alloy materials were melted to form ingots thereofrespectively (thickness: 500 mm). The materials had the followingcompositions respectively:

[0047] A3003 Material:

[0048] Si: 0.58 mass %; Fe: 0.68 mass %; Cu: 0.18 mass %; Mn: 1.48 mass%; Mg: 0.02 mass %; Zn: 0.09 mass %; Al and unavoidable impurities: q.s.

[0049] A3004 Material:

[0050] Si: 0.58 mass %; Fe: 0.68 mass %; Cu: 0.20 mass %; Mn: 1.48 mass%; Mg: 1.01 mass %; Zn: 0.23 mass %; Al and unavoidable impurities: q.s.

[0051] (2) Formation of Plate Material

[0052] Plate materials each having a thickness as shown in Table 1 weremade according to the methods having the following conditionsrespectively:

[0053] Process of the Invention (A):

[0054] Each ingot was subjected to a soaking treatment at 600° C. for 6hours in a holding furnace, followed by hot rolling at a temperature atthe beginning of rolling of 550° C. and under temperature control suchthat the temperature at the end of rolling is as shown in Table 1. Theresulting product was used as such as a plate material.

[0055] Process of the Prior Art (B):

[0056] Each ingot was subjected to a soaking treatment at 600° C. for 6hours in a holding furnace, followed successively by hot rolling at atemperature at the beginning of rolling of 550° C. and under temperaturecontrol such that the temperature at the end of rolling is 310° C. andcold rolling at 80° C.

[0057] Subsequently, the resulting workpiece was subjected successivelyto process annealing at a temperature of 360° C. for 3 hours, coldrolling at a temperature of 80° C., and a heat treatment at 230° C. for3 hours. Then, the thus treated workpiece was used as a plate material.

[0058] (3) Determination of Properties

[0059] Loss of Proof Stress (%) After Baking Finish Treatment:

[0060] Proof stress (Γ₀) and elongation of each plate material weredetermined before the baking finish treatment.

[0061] Subsequently, a fluorine coat was applied to each plate material,and the resulting plate material was subjected to baking finishtreatment at a temperature as shown in Table 1 to measure proof stress(F) and elongation after the treatment.

[0062] Loss of proof stress (%) after the baking finish treatment wascalculated according to the following equation: 100×(Γ₀-Γ)/Γ₀.

[0063] The results are as shown in Table 1.

[0064] Area Ratio of Recrystallized Grain Structure:

[0065] Grain structures were observed according to the Barker's method.

[0066] More specifically, each plate material was ground to expose thesurface of the plate material, and the thus exposed surface wassubjected to electropolishing. The polished surface was etched using anHBF₄ solution, followed by polariscopic image data processing tointegrate the surface area of the grains of the recrystallizedstructure. Then, rate (percentage) of the integrated value within ascope (5 mm×5 mm) was determined. The results are shown in Table 1.

[0067] Meanwhile, referring to plate materials of Example 9 andComparative Example 8, photomicrographs (50 power) of them are shown inFIGS. 4 and 5 respectively.

[0068] (4) Bending Test

[0069] Each plate material having been subjected to baking finishtreatment was bent to visually observe whether or not there occurredrough surface (lifting of the coating) and cracking.

[0070] With respect to determination of rough surface, each platematerial was bent in two modes, i.e. orthogonal to the rolling direction4 (in the longitudinal direction of the plate material) as shown in FIG.6 and parallel to the rolling direction (in the width direction of theplate material) as shown in FIG. 7, to determine bending angles whenoccurrence of rough surface was observed.

[0071] Meanwhile, with respect to determination of cracking as shown inFIG. 7, each plate material was bent by 90° and 180° parallel to therolling direction (in the width direction of the plate material) toobserve whether or not there occurred cracking.

[0072] In Table 1, ∘ means that there occurred no cracking; Δ means thatthere occurred slight cracking that is not significant in practicaluses; and × means that notable cracking occurred. TABLE 1 Formation ofplate material Baking Finish Property Property Temp. at the Plate(before baking) (after baking) Kind of end of thickness Proof stressBaking Proof stress Alloy Process rolling (° C.) (mm) (N/mm²) Elongation(%) temp. (° C.) (N/mm²) Elongation (%) Example 1 A3003 A 290 1.5 14626.2 180 146 27.1 Example 2 A3003 A 290 1.5 146 26.2 260 141 27.6Example 3 A3003 A 290 5.0 142 26.5 260 138 27.4 Example 4 A3003 A 3001.0 137 26.5 260 136 27.2 Example 5 A3003 A 310 1.5 125 28.5 200 12528.9 Example 6 A3003 A 310 3.0 124 28.6 200 123 29.1 Example 7 A3003 A310 5.0 123 28.8 200 122 29.1 Example 8 A3003 A 310 1.5 125 28.5 260 12429.0 Example 9 A3003 A 310 3.0 124 28.6 260 122 29.5 Example 10 A3003 A310 5.0 123 28.8 260 121 29.8 Example 11 A3003 A 310 3.0 124 28.6 300120 30.0 Example 12 A3003 A 330 1.5 114 30.4 200 114 30.6 Example 13A3003 A 330 1.5 114 30.4 260 112 31.4 Example 14 A3003 A 340 5.0 10531.0 260 103 32.0 Example 15 A3003 A 340 6.0 104 31.2 260 102 32.3Example 16 A3003 A 340 5.0 105 31.0 300 99 32.7 Comparative A3003 A 2503.0 170 19.8 260 168 21.2 Example 1 Comparative A3003 A 310 3.0 124 28.6340 85 33.6 Example 2 Comparative A3003 A 330 3.0 106 31.0 340 78 38.1Example 3 comparative A3003 A 360 3.0 87 33.3 260 82 34.1 Example 4Comparative A3003 B 310 3.0 95 34.1 180 94 34.1 Example 5 ComparativeA3003 B 310 3.0 95 34.1 260 93 34.3 Example 6 Comparative A3004 B 3103.0 225 8.8 180 20 8.8 Example 7 Comparative A3004 B 310 3.0 225 8.8 260160 15.2 Example 8 Comparative A3004 B 310 3.0 225 8.8 340 77 22.0Example 9 Bending test Baking finish Rough surface Surface ratioOrthogonal Parallel to Cracking of recrystallized Loss of to the rollingthe rolling 90° 180° grain structure (%) proof stress (%) direction (°)direction (°) Bending Bending Example 1 0 0 none 180 ◯ Δ Example 2 0 3.4none 180 ◯ Δ Example 3 0 2.8 none 180 ◯ Δ Example 4 0 0.7 none 180 ◯ ΔExample 5 0 0 none 180 ◯ ◯ Example 6 0 0.8 none 180 ◯ ◯ Example 7 0 0.8none 180 ◯ ◯ Example 8 0 0.8 none 180 ◯ ◯ Example 9 0 1.6 none 180 ◯ ◯Example 10 0 1.6 none 180 ◯ ◯ Example 11 0 3.2 none 180 ◯ ◯ Example 12 00 none 180 ◯ ◯ Example 13 0 1.8 none 180 ◯ ◯ Example 14 5 1.9 none 180 ◯◯ Example 15 5 1.9 none 180 ◯ Δ Example 16 0 5.7 none 180 ◯ ◯Comparative 0 1.2 none 180 X X Example 1 Comparative 55 31.5 180 140 ◯ ◯Example 2 Comparative 60 26.4 180 140 ◯ ◯ Example 3 Comparative 80 5.7110 110 ◯ ◯ Example 4 Comparative 100 1.1 140 140 ◯ ◯ Example 5Comparative 100 2.1 140 110 ◯ ◯ Example 6 Comparative 100 10.7 110 110 XX Example Comparative 100 28.9 140 110 X X Example 8 Comparative 10065.8 140 110 Δ X Example 9

[0073] The following became apparent from Table 1:

[0074] (1) As is clearly shown in a comparison between Example 9 andComparative Example 6, using the same material and the same temperatureat the end of rolling and having the same plate thickness, ComparativeExample 6, obtained through hot rolling, followed by cold rolling,process annealing, etc., came to have a proof stress lower than 95 N/mm2after the baking finish treatment, which is lower than that of Example 9in spite of the same baking finish temperature of 260° C. In addition,in the bending test, Comparative Example 6 was more likely to have roughsurface than Example 9. This is because the structure of ComparativeExample 6 was converted into recrystallized grain structure through aseries of steps after the hot rolling and further during the bakingfinish treatment.

[0075] The above description obviously shows effectiveness of theprocess of the present invention employing only hot rolling underconditions where even the subsequent baking finish treatment does notinduce growth of recrystallized grain structure.

[0076] (2) A fiber structure and a finely divided secondary structure(subgrains) coexist in Example 9 after the baking finish treatment asshown in FIG. 4, and Example 9 showed a high proof stress of 122 N/mm²and a high elongation of 29.5% after the baking finish treatment but avery low proof stress loss of 1.6%, thus showing excellent results inthe bending test.

[0077] Meanwhile, a coarse recrystallized grain structure was observedinstead of the fiber structure in Comparative Example 8 shown in FIG. 5.Although Comparative Example 8 showed a high proof stress of 160 N/mm²after the baking finish treatment, it showed a small elongation of 15.2%and an extremely great % loss of proof stress. As a result, there wereobtained significantly bad results in the bending test in terms of roughsurface and cracking.

[0078] The above description obviously shows effectiveness of thearchitectural Al alloy material according to the present inventioncontaining a mixture of a fiber structure and a finely divided secondarystructure.

[0079] As is clearly explained above, the hot rolled A3003 materialobtained under control such that the temperature at the end of rollingbe in the range of 290 to 340° C. maintained the state that it containssubstantially the fiber structure with no growth of recrystallized grainstructure even after the baking finish treatment, and it also showed aproof stress loss of 10% or less and also secured an absolute proofstress value of 95 N/mm² or more and an elongation of 27% or more.Therefore, the Al alloy material according to the present inventionenjoys high industrial value as a building material having excellentbendability and undergoing no loss of proof stress.

[0080] It should be noted here that while the baking finish treatmentwas carried out in a temperature range of 260 to 280° C. in the abovedescription, the architectural Al alloy material according to thepresent invention can be employed suitably whether the temperature ofthe baking finish treatment is 260° C. or lower or in the range of 280to 300° C.

What is claimed is:
 1. An architectural Al alloy material, which is ahot rolled material defined by JIS A3003 (3003 defined by B209 of ASTM);the material comprising, in terms of a structure after a baking finishtreatment at a temperature of not higher than 300° C., a fiber structureand a recrystallized grain structure having an area ratio of 20% orless; wherein the material undergoes a proof stress loss of 10% or lessafter the baking finish treatment.
 2. The architectural Al alloymaterial according to claim 1, having a proof stress and an elongationof 95 N/mm² or more and 27% or more, respectively, after the bakingfinish treatment.
 3. The architectural Al alloy material according toclaim 1 or 2, wherein the baking finish treatment is carried out at atemperature of 260 to 280° C.
 4. A process for manufacturing anarchitectural Al alloy material comprising the steps of: subjecting aningot of JIS A3003 (3003 defined by B209 of ASTM) to a soakingtreatment; and subjecting the resulting ingot to hot rolling to becarried out in such a way that it has a temperature of 290 to 340° C. atthe end of rolling; wherein the thus treated ingot is as such applied toa practical use.